The present invention relates generally to hydraulically-actuated fuel injection systems, and more particularly to pressure-intensified hydraulically-actuated fuel injection systems with direct control needle valves.
There has been a continuing trend in internal combustion engine design to independently control fuel injection timing and duration in order to improve performance and decrease undesirable emissions. One method of decoupling the operation of the fuel injection system from the rotation angle of the engine is to utilize hydraulically-actuated fuel injectors that are electronically controlled in their operation. In this way, virtually any amount of fuel can be introduced into an individual engine cylinder at any time in the engine cycle.
Caterpillar Inc. of Peoria, Ill. has experienced considerable success in the incorporation of its common rail hydraulically-actuated fuel injection systems in a range of diesel engines. While these hydraulic systems have performed magnificently for many years, some engine applications are not particularly well suited to the use of common rail hydraulic systems for a variety of reasons known in the art. For example, one class of relatively large diesel engines utilize heavy fuel oil that by its normally highly viscous nature renders it generally unsuitable for common rail type fuel injection systems.
In another type of fuel injection system, a conventional cam driven plunger is used to pressurize fuel, but control over each injection event is initially maintained by spilling fuel to control the time at which fuel pressure reaches injection levels. However, those skilled in the art will appreciate that some engines and/or engine applications are not particularly well suited to the positioning of a cam shaft in close proximity to the fuel injectors.
In still another class of engines, a conventional pump and lines system is employed. These systems utilize individual cam driven mechanical unit pumps spatially separated from injection nozzles but fluidly connected via individual high pressure fuel lines. These systems often lack electronic control and undesirably require the plumbing of cyclically high pressure fuel around a hot engine.
Thus, while the specific fuel system capabilities of different engines vary, there remains a continuing trend toward introducing electrical control in order to improve engine performance and decrease undesirable emissions. While this trend has been more forthcoming in the field of engines that burn distillate diesel fuel, this trend has been more difficult to accomplish in the relatively large class of diesel engines that burn residual fuels, such as heavy fuel oil. Heavy fuel oil injection systems remain more resistant to the incorporation of electronic controls in part because of the necessity to isolate the heavy fuel plumbing from the electronic systems while retaining a coupling between the electronic actuators and the flow of heavy fuel oil within the individual injection systems.
The present invention is directed to overcoming these and other problems associated with fuel injection systems.
A fuel injection system includes a plurality of mechanical unit pumps, each having a pump outlet. A pressure-intensifying hydraulically-actuated electronically-controlled fuel injector is provided for each of the plurality of mechanical unit pumps. Each of the fuel injectors has a direct control needle valve and an injector body that defines an actuation fluid inlet, a fuel inlet, an actuation fluid cavity and a fuel pressurization chamber. Each fuel injector includes a moveable pumping element with a large hydraulic surface exposed to fluid pressure in the actuation fluid cavity and a small hydraulic surface exposed to fluid pressure in the fuel pressurization chamber. An actuation fluid supply line is provided for each of the plurality of mechanical unit pumps, and each supply line fluidly connects one pump outlet to one actuation fluid inlet.